superio/nuvoton: Add back Nuvoton NCT6776 support

Revert commit 53552cc0 (Drop SuperIO nuvoton/nct6776),
removing the code as no other mainboard uses it.

The board Intel Saddle Brook uses this device, so add the
code back with minor adaptations.

Change-Id: I546879285ad8336e81798d0fbdf94f72e1fa61a2
Signed-off-by: Teo Boon Tiong <boon.tiong.teo@intel.com>
Reviewed-on: https://review.coreboot.org/16519
Tested-by: build bot (Jenkins)
Reviewed-by: Martin Roth <martinroth@google.com>
6 files changed